Alkylhalosilanes and arylhalosilanes are valuable precursors to silicones and organofunctional silanes that are used in a broad range of industries. Methyl-chlorosilanes and phenylchlorosilanes are particularly valuable and are the most commonly manufactured products of these classes. Manufacture is done using the Rochow-Müller Direct Process (also called Direct Synthesis and Direct Reaction), in which copper-activated silicon is reacted with the corresponding organohalide in a gas-solid or slurry-phase reactor at a temperature and pressure sufficient to effect the desired reaction rate and stability, and product selectivity and yield. Fluidized-bed reactors are the gas-solid reactors most often used. The silicon-containing reaction products are organohalosilanes (R1aSiXb), organohalohydrosilanes (R1cSiHdXe), halosilanes (HfSiXg), organohalodisilanes (R1hNXjSiSiXkR1l), organohalopolysilanes (R1mXqSi—(Si(R1X))n—SiXqR1m) and carbosilanes (R1X2Si—CH2—SiXR12, R1X2Si—CH2—CH2—SiX2R1 and other similar compounds). Carbosilanes with a single —CH2— group between the silicon atoms are also called silylmethylenes or disilamethanes.
Organohalosilanes have the general formula, R1aSiXb, wherein R1 is a saturated or unsaturated aromatic group, a saturated or unsaturated aliphatic group, alkaryl group, or cycloaliphatic hydrocarbyl group such as methyl, ethyl or phenyl, X is a halogen atom such as chlorine or bromine and a and b are positive integers with the proviso that the sum, (a+b)=4.
Organohalohydrosilanes have the general formula, R1cSiHdXe, in which R1 and X have the same meaning as above. The subscripts, c, d and e are positive integers satisfying the sum, (c+d+e=4).
In the halosilanes, (HfSiXg), f≧0 and g is an integer such that (f+g=4). X is a halogen atom as defined above.
Organohalodisilanes contain one Si—Si bond as indicated in the general formula, (R1hXjSiSiXkR1l). R1 and X have the same meanings as defined above. The subscripts, h, j, k and l are individually ≧0 with the sums (h+j=3) and (k+l=3). By extension, trisilanes contain Si—Si—Si units and polysilanes have more than three catenated Si atoms.
Hot effluent exiting from the fluidized-bed reactor, in which copper-activated silicon is undergoing reaction with an organohalide, comprises a mixture of copper, metal halides, silicon, silicides, carbon, gaseous organohalide, organohalosilanes, organohalodisilanes, carbosilanes and hydrocarbons. This mixture is first subjected to gas-solid separation in cyclones and filters (see U.S. Pat. No. 4,328,353). The gaseous mixture and ultrafine solids are condensed in a settler or sludge tank from which the organohalide, organohalosilanes, hydrocarbons and a portion of organohalodisilanes and carbosilanes are evaporated and sent to fractional distillation. The ultrafine solids accumulate in the settler along with the less volatile silicon-containing compounds and this mixture (sludge) is purged periodically and sent to waste disposal or to secondary treatment for the recovery of monomers from the liquid fraction.
Three silicon-containing solid wastes are produced from the fluidized-bed. Elutriated solids, which are trapped by the cyclone or filters, are called cyclone fines or cyclone solids. Those particulates which escape the cyclones and collect in the settler are called ultrafines, settler solids or revaporizer solids. The third category is the solid, which remains unreacted in the fluidized-bed at the end of a campaign. This is called spent mass or spent contact mass. Typically, spent mass has a larger average particle size and wider particle size distribution than cyclone solids and cyclone solids are larger than ultrafines. Spent mass and cyclone fines are dry solids, which can be pyrophoric. Ultrafines are wet and agglomerate into a sludge. For this reason, ultrafines are sometimes called sludge.
A world-class methylchlorosilane plant disposes of thousands of tons of ultrafines, cyclone solids and spent mass per year at considerable cost and loss of raw material values. There are also environmental impacts of the waste disposal methods employed. Accordingly, it is desirable to recover value from these waste solids. Methods of reusing the solids for copper recovery, for production of chlorosilanes, alkoxysilanes, methylchlorosilanes and phenylchlorosilanes have been disclosed in the patent and journal literature.
Passivation of cyclone solids for safe landfill disposal or later recovery of copper is disclosed in U.S. Pat. No. 5,342,430.
U.S. Pat. No. 2,803,521 discloses a method to separate and recover silicon and copper from spent reaction masses. Soucek, et al., (Chem. Abstr. vol. 64 (1966) 17638c) and Kopylov, et al., (Chem. Abstr. vol 75 (1971) 14421g) disclose metallurgical processes for copper recovery from roasted spent masses.
Rathousky, et al. (Chem. Abstr. vol 81(1974) 78008) reported the Direct Synthesis of phenylchlorosilanes using spent mass from the Direct Synthesis of methylchlorosilanes. Takami, et al (Chem. Abstr., vol 89(1978) 509946) disclosed a similar Direct Synthesis of phenylchlorosilanes from methylchlorosilane spent mass that was first heated to 500-900° C.
Ritzer, et al (U.S. Pat. No. 4,390,510) and others have shown that reaction of cyclone fines with HCl produces trichlorosilane and silicon tetrachloride. Reaction with alcohols produces alkoxysilanes. These uses of cyclone solids are cited in Catalyzed Direct Reactions of Silicon, K. M Lewis and D. G. Rethwisch (Editors), Elsevier, N.Y. 1993, pages 28-29 and refs cited therein.
U.S. Pat. No. 5,712,405 discloses collection of cyclone fines and filtered fines and recycling them to the bottom of the fluidized bed reactor for further reaction with an organohalide to produce organohalosilanes.
U.S. Pat. No. 6,465,674 discloses introducing cyclone fines into liquid silanes and reinjection of that suspension into the fluidized bed for Direct Synthesis of chloro or organocholorosilanes.
U.S. Pat. No. 4,224,297 discloses a method for the reuse of spent mass with a maximum particle size of 50 microns comprising heating it at 100-350° C. in air or nitrogen for at least 15 hours prior to reacting it with methyl chloride to produce methylchlorosilane monomers.
All of the foregoing references dealing with synthesis of organohalosilanes from cyclone fines and spent mass comprise gas-solid reactions in two phase reactors. Those cited below are all done in three-phase reactors, such as mechanically agitated slurry reactors and bubble columns.
British Patent, GB 1,131,477 claims a process for the preparation of alkylhalo-silanes comprising suspending a contact mass composition in an inert liquid, such as a halogenated aromatic hydrocarbon, at a temperature greater than 175° C. and reacting it with an alkyl halide to produce alkylhalosilanes.
U.S. Pat. No. 7,153,991 discloses the slurry-phase Direct Synthesis of organohalosilanes comprising preparing a slurry of nanosized copper catalyst and silicon, 90 percent of which is between about 1 to about 300 microns, in a thermally stable organic solvent and followed by reaction with an organohalide at temperature greater than 250° C.
Application WO 2012/080067 deals with reaction of finely divided solid residues from the Direct Synthesis of methylchlorosilanes with chloroalkanes in a liquid reaction medium. The finely divided solid residues have silicon content greater than fifty percent and maximum particle size 200 microns, preferably maximally 100 microns. The liquid reaction medium is preferably aprotic and thermally stable. WO 2012/080067 is illustrated with silicon of unspecified particle size that was thermally activated with an unspecified catalyst and promoter(s) to contain catalytically active intermetallic phases. According to WO 2012/080067, this silicon was first suspended in Silicone Oil AP100 (a poly(phenylmethylsiloxane, CAS #63148-58-3)) and reacted with methyl chloride in a stirred autoclave at 3 bar and 350° C. for 110 minutes; solid residue from this reaction was recovered and reacted with methyl chloride, apparently also at 3 bar and 350° C., in a fluidized bed containing Silicone Oil AP100 for 14 minutes; the principal reaction products were dimethyldichlorosilane and trimethylchlorosilane, the former being 2.7 to 4.7 times more than the latter; when the pressure was increased to 10 bar (Example 3), trimethylchlorosilane became the main product, the ratio being 6.1.
In the conclusion to Example 3 of WO2012/080067, it states that “the selectivity to the alkylchlorosilanes can be influenced in a targeted manner via the solubility of methyl chloride in the liquid reaction medium, adjusted by means of the reaction medium and the overpressure, so that trimethylchlorosilane (M3) is the main product of the reaction.” It will be shown by examples hereinbelow that trimethylchlorosilane formation in the illustrative experiments of WO 2012/080067 arises from the cleavage of trimethylsilyl groups from Silicone Oil AP100 and is unrelated to the reaction of methyl chloride with the silicon residue.
It is understood by Applicants that WO 2012/080067 states at page 5, line 6 that the disclosed process “constitutes a further direct synthesis” (Application in German, translation into English). In 1967, R. J. H. Voorhoeve (Organohalosilanes: Precursors to Silicones, Elsevier, Amsterdam, 1967. Pages 144-145 and ref 177 on page 151) reported that silicone oils and paraffins had been tried as solvents in the slurry-phase Direct Synthesis of organohalosilanes in 1962-1963, but they had been found not to be inert under the reaction conditions. The silicone oils decomposed to give volatile compounds and the paraffins yielded appreciable quantities of tar. The methylchlorosilane reaction product consisted mostly of trichlorosilane and methyltrichlorosilane.
As the foregoing review of the literature shows, there have been many attempts in the past to recover value, particularly methylchlorosilane monomers, from spent mass and cyclone solids produced during the Direct Synthesis of methylchlorosilanes. None of these attempts has resulted in a reliable process that produces a composition of highly valued methylchlorosilanes and methylchlorohydrosilanes.
U.S. Pat. No. 5,338,876 discloses the Direct Synthesis of allylchlorosilanes in stirred-bed and fluidized-bed reactors at 220-350° C. and 1-5 atmospheres, preferably 300-330° C. and 1-3 atmospheres. The disclosure is particularly directed to the Direct Synthesis of allyldichlorosilane by reacting fresh silicon metal with mixtures of allyl chloride and hydrogen chloride, wherein the hydrogen chloride is in molar excess. A companion journal publication with this information is Yeon, et al (Organometallics, vol 12 (1993), pp 4887-4891). Other literature references to the Direct Synthesis of allylhalosilanes in fixed, stirred or fluidized bed reactors with fresh silicon metal are the following: Voorhoeve, Organohalosilanes: Precursors to Silicones, page 203-204; Petrov, et al., Synthesis of Organosilicon Monomers, pp 44-46 and in Table 5, page 55.
Allylhalosilanes are useful intermediates for the synthesis of organic specialties as well as for the synthesis of sulfur-silanes useful in tire and rubber applications. A particularly valuable intermediate is allyltrichlorosilane, which can be converted to allyltriethoxysilane for the synthesis of sulfur-containing silanes.
The polymerization of diallylsubstrates, including diallyldimethylsilane, is reported in the following: Forbes, et al., J. Amer. Chem. Soc., vol 114 (1992) pp 10978-10980; Marvel, et al., J. Org. Chem., vol. 25 (1960) pp 1641-1642; Butler, et al., J. Org. Chem., vol. 25 (1960) pp 1643-1644.